The present invention relates to a method of continuous extraction of particulate solid materials, particularly vegetable or animal raw materials.
Methods of the above mentioned general type are known in the art. In known methods for recovery of extracts from vegetable or animal raw materials, solvent extraction is especially highly profitable. Conventionally, hexane or heptane are used as the solvent. This method possesses, however, the disadvantage of high apparatus and energy expenses which are used for recovering the solvent from the extract and the extract-poor solid material residues. Moreover, the conventional solvent is explosive. It has been known for a long time that these disadvantages can be avoided with the utilization of highly compressed gases as solvents. Certain gases in condition in the region of their critical points are transformed to solvents and their receptability for extracts is many times higher than can be expected from the respective vapor pressure values. These gases include health-acceptable non-explosive gases such as carbon dioxide and sulfur hexafluoride. Also, ethylene, propane, butane and isobutane are proposed as solvents. In addition to the health-acceptability and non-explosiveness, these solvents have the further advantage that in normal conditions they are gaseous and after extraction can be separated in a very simple and basic manner from the extract and the extract-poor solid material residues by vaporization. These processes are described in the German Pat. No. 1,493,190.
Continuous extraction of solid material with highly compressed gases is possible only when a container under high pressure is continuously charged with the solid material. In the absence of such charging devices, which must overcome pressure differences greater than 50 bar, the high pressure extraction of solid materials has been carried out only by separate charges. The expensive apparatus and personnel costs which result from the discontinuous operation are of great disadvantage for the high pressure extraction as compared with the extraction in condition of normal pressure.
The DE-AS 2,827,002 describes the possibility of a continuous extraction with utilization of high pressure sluices. Various experiments described in this reference are carried out, also by charges, with no hint of the technical realization of the above mentioned sluices given in this reference.
A continuous fluid device for fine-grain to dust-like solid materials in a reaction chamber under high pressure is known from the coal gasification and described in the DE-OS 2,648,048. A pressure differential of approximately 40 bar is overlapped here by condensing a mixture of coal and carbonic acid snow, separating the carbon dioxide by sublimation, and supplying the solid material into the reaction chamber. In this process the carbon dioxide is used as auxiliary means for continuous supplying of a solid material into a pressure container, in solid form as carbonic acid snow. Moreover, this reference does not provide any information about discharge of a residue from the reaction chamber.
The continuous extraction of caffeine from coffee with the highly compressed dioxide is disclosed in the DE-OS 2,638,383. In the process described there, a water solution is produced first from which the caffeine is then extracted. Here also a liquid-liquid extraction takes place.
The DE-OS 3,016,917 describes a semi-continuous method. The solvent continuously flows in circulation with the solid material in several pressure containers connected in series with one another, and the container is charged and emptied in charged manner.